drivers/bios_emulator: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/bios_emulator/Makefile b/drivers/bios_emulator/Makefile
index 90c64da..c73da97 100644
--- a/drivers/bios_emulator/Makefile
+++ b/drivers/bios_emulator/Makefile
@@ -6,7 +6,7 @@
 
 $(shell mkdir -p $(obj)$(X86DIR))
 
-COBJS	= atibios.o biosemu.o besys.o bios.o \
+COBJS-$(CONFIG_BIOSEMU)	= atibios.o biosemu.o besys.o bios.o \
 	$(X86DIR)/decode.o \
 	$(X86DIR)/ops2.o \
 	$(X86DIR)/ops.o \
@@ -14,6 +14,7 @@
 	$(X86DIR)/sys.o \
 	$(X86DIR)/debug.o
 
+COBJS	:= $(COBJS-y)
 SRCS	:= $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))